Technical Field
The present disclosure relates to a light emitting device that makes use of a light emitting element, and to a lighting fixture in which this light emitting device is used.
Related Art
A package-type light emitting device in which a plurality of light emitting elements (semiconductor light emitting elements) are mounted on a metal substrate or a ceramic substrate in a high-output type of semiconductor light source has been proposed in the past as prior art.
The finished product is incorporated in a lighting fixture in which one or more of these light emitting devices are used, a heat dissipation path is set up so that the heat generated by the light emitting elements is not trapped inside the light emitting devices, and good dielectric strength is ensured (see, JP2008-218761A).
When the conventional light emitting device discussed above is actually incorporated into a lighting fixture, the dielectric strength is lower with a metal substrate package. And with a conventional light emitting device, if an attempt is made to ensure good dielectric strength, heat dissipation performance may end up suffering if an insulating sheet is sandwiched at the rear face of the light emitting device, for example. Also, with a conventional light emitting device, the sheet surface area has to be large enough to achieve an adequate creepage distance to the end of the metal substrate, and this hampers efforts to make the device more compact, and makes it difficult to achieve both good heat dissipation and good dielectric strength.
Meanwhile, with a ceramic substrate package with high dielectric strength, the higher is the output, the lower is the thermal conductivity, and consequently heat can become trapped inside the light emitting device, which is a problem in that it reduces efficiency and shortens the service life.
Also, just as with a metal substrate package, raising the dielectric strength requires a larger creepage distance from the power supply terminal to the ceramic substrate end face, and this makes it harder to reduce the size.
In view of this, there has also been disclosed a light emitting device that is more compact and has a discharge suppressor that increases the creepage distance on the mounting board on which the light emitting element is mounted see, JP2013-38430A). With this light emitting device, a discharge suppressor is formed so as to gain creepage distance by providing fine texturing around the periphery of the board on which the light emitting element is mounted. Also, with this light emitting device, the mounting board that is used is installed in a metal body formed by aluminum die casting, for example.
With a conventional light emitting device, the mounting board is preferably made of a ceramic member that has good insulation properties, has at least a certain level of thermal conductivity, and is low in cost, such as alumina. With a conventional light emitting device, however, the thermal conductivity of the ceramic material used for the mounting board is only about ⅓ to 1/20 that of a metallic material, so particularly in applications where a high output (10 W or higher) is applied, if the light emitting element and the light emitting device are directly mounted to a mounting board such as this, heat dissipation will be unsatisfactory, and performance and service life will suffer. In addition, with a conventional light emitting device, if the alumina substrate used as the mounting board is made thinner in order to lower thermal resistance, the brittleness that is characteristic of ceramics can result in warping, sagging, and other such problems.
Also, with a conventional light emitting device, it has been said that a plurality of walls are provided in a protruding shape, or fine recess portions are made, so as to surround the board surface in order to gain creepage distance, but fine machining of a board surface is difficult and can increase the risk of cracking or chipping, so the desired creepage distance may not be achieved.
Also, with a conventional light emitting device, to ensure heat dissipation, as discussed above, the board thickness has to be reduced, which means that any grooves made in that board cannot be as deep, so the creepage distance has to be gained by the height of the protruding walls. Raising the wall height is disadvantageous in terms of cost and workability, and also leads to lower light emission efficiency due to blockage of light in the lateral direction of the light emitting element.